A fuel cell stack is constituted of single cells stacked, and each of the single cells includes a membrane electrode assembly and a pair of separators with corrugated shapes that sandwiches the membrane electrode assembly. Further, the single cells are stacked between two end plates and are added a fastening load of a fastening bolts and/or a casing in a stacking direction to form the fuel cell stack.
A gas channel is formed between the membrane electrode assembly and a separator of the pair of the separators along a reaction surface, and a cooling medium channel is formed between two separators lying next to each other. Further, a sealing member is provided on a periphery of the membrane electrode assembly to prevent a leakage of gas or the like.
The Patent Document 1 of JP 2011-146247 A discloses that while a surface of an electrode layer of each of the single cells is subject to pressure unevenly, a terminal voltage is sometimes reduced due to an increase of a contact resistance, and an abnormality of fuel cell single cells can therefore be detected by means of strain gauges provided on the surfaces of metal separators before occurrence of performance deterioration or fluid leakage.